1. Field of the Invention
The present invention is in the field of muffling apparatus used to reduce the sound emitted by internal combustion engines. More particularly, the present invention involves methods and systems for muffling the sound emitted by internal combustion engines while maintaining low back pressure for improved power and fuel economy. The methods and systems employ a bed of silica, alumina or other appropriate particulate material for absorbing and/or disrupting sound waves.
2. Review of the Relevant Technology
Internal combustion engines are ubiquitous in modern life but have the drawback of producing considerable noise, particularly from the exhaust pipe. To effectively muffle and reduce engine noise to within acceptable levels, exhaust pipes are typically equipped with sophisticated channeling and baffling schemes. Because muffling systems typically involve restricting the free flow of exhaust gasses in order to disrupt or otherwise dampen the sound waves generated by the operation of the engine, mufflers can create significant xe2x80x9cback pressurexe2x80x9d, known to reduce fuel economy and power. The use of catalytic converters in-line with conventional muffling systems further increases back pressure.
Back pressure inherently reduces fuel economy and engine power by increasing the amount of work that the engine must perform just to emit the waste exhaust gases into the air. It also reduces power by generally requiring an increase in the fuel to air ratio that is fed into the cylinders in order for the engine to run properly. Conversely, reducing back pressure, such as by the use of expensive xe2x80x9cheadersxe2x80x9d or other muffling systems rather than conventional mufflers allows for a leaner fuel/air mixture, thus resulting in greater generation of power per quantity of fuel used. Reducing back pressure also reduces the amount of work that the engine must perform to emit waste exhaust gases. Unfortunately, headers or other low back pressure muffling systems are costly and generally not approved for conventional vehicles, but are reserved for racing vehicles, because they do not meet present noise reduction standards.
In view of the requirement that vehicles with internal combustion engines must be equipped with muffling systems which meet relevant government noise reduction standards, but in view of other standards relating to the need to reduce pollution and improve fuel economy, there is inherently a tension or conflict with noise reduction goals, on the one hand, and fuel economy and emissions reduction, on the other. The result of this tradeoff is generally reduced power and vehicular performance.
It is obvious that improving fuel economy generally reduces the quantity of emissions produced by a vehicle. It is also true that deriving more power per quantity of fuel generally translates into better fuel economy and reduced emissions. One way to do this would be to reduce the back pressure resulting from conventional muffling systems. The problem with this strategy is that there are presently no reasonably priced or sized muffling systems that are capable of significantly reducing back pressure while satisfying present vehicle noise standards.
Another source of back pressure are in-line catalytic converters, which are required in order to reduce emissions from gasoline powered vehicles. Although catalytic converters themselves might not create as much back pressure as conventional mufflers, the back pressure imparted by a catalytic converter is cumulative to the back pressure created by the muffler in the same exhaust system, thus further reducing fuel economy and engine power.
In view of the foregoing, it would be an significant advancement in the art to provide improved methods and systems for effectively and inexpensively muffling the sound emitted by internal combustion engines while substantially reducing back pressure compared to conventional mufflers.
It would be a further advancement in the art to provide methods and systems for muffling the sound emitted by internal combustion engines which were simultaneously capable of substantially reducing back pressure compared to conventional mufflers while meeting or exceeding present noise reduction standards.
It would be a tremendous advancement in the art if such methods and systems for muffling the sound emitted by internal combustion engines were capable of reducing back pressure so as to improve fuel efficiency and increase engine power, while also providing equal or greater muffling of engine sounds compared to conventional mufflers.
Finally, it would be an enormous advancement in the art if such methods and systems for muffling the sound emitted by internal combustion engines were adaptable so as to also be capable of reducing pollutants found in exhaust emissions such that they provided the duel purpose of reducing engine noise and engine pollution.
Such methods and systems for muffling the sound emitted by internal combustion engines while reducing back pressure, increasing engine power and, optionally, reducing engine emissions are disclosed and claimed herein.
The present invention encompasses improved methods and systems for muffling engine sounds emanating from the exhaust system of internal combustion engines. Such muffling methods and systems employ a muffling chamber filled with an appropriate particulate media capable of absorbing or otherwise disrupting the sound waves found in the exhaust stream corresponding to engine noise. Because moving exhaust gases are able to more freely pass through the spaces between the individual particles comprising the particulate media than through baffling and dampening devices found in conventional mufflers, the muffling systems of the present invention are able to muffle sound while reducing back pressure compared to conventional mufflers. In turn, greatly reducing the back pressure substantially improves the power and fuel efficiency of the engine.
The inventive muffling systems according to the invention preferably include one or more exhaust muffling chambers, which include muffling particles disposed therein, in gaseous communication with an internal combustion engine. The sound waves generated by the explosions within the cylinders of internal combustion engines are concentrated within and directed through the exhaust pipes or conduits connected to the engine. As the exhaust gases pass through the one or more exhaust muffling chambers the sound waves contained therein and propagated thereby are widely scattered, and thus dissipated and muted, by the surrounding particulate media. More particularly, a diffusion pipe is at least partially sunk beneath a volume of muffling particles so that the exhaust gases are passed from the diffusion pipe into the surrounding muffling particles. It is believed that the particulate muffling particles act to scatter and redistribute the sound waves throughout the muffling chamber in a manner that causes a substantial portion of the sound waves to become substantially out of phase and thus able to cancel each other out. This reduces the amplitude and, hence, the volume of the sound represented by the at least partially cancelled out sound waves.
An example of an appropriate particulate material capable of muffling sound from an internal combustion engine is silica sand. Another is alumina. Silica and alumina are preferred because they are also capable of catalytically degrading waste gases and particulates found in the exhaust gases from internal combustion engines, as more fully explained: in U.S. Pat. No. 5,928,618 and co-pending U.S. application Ser. Nos. 09/257,458 and 09/307,145. For purposes of disclosing methods and systems for catalytically degrading unburnt particulates and hydrocarbons in waste exhaust gases from an internal combustion engine and other systems that burn fossil fuels, the foregoing patent and applications are incorporated herein by specific reference.
In addition to providing catalytic degradation of unburnt hydrocarbons in waste exhaust gases, silica sand is also preferred because of its extremely low cost and ready availability. Nevertheless, virtually any particulate having an average particle size from about 0.0.1 mm to about 1 cm would work in muffling the sounds emitted by internal combustion engines. Particles having a size in a range from about 0.1 mm to about 5 mm are especially preferred. Virtually any geologic material can be ground and graded into appropriate particles within the scope of the present invention. In addition, synthetically formed spheres or other particles, such as ceramic, glass or metallic spheres, are certainly within the scope of the present invention. The muffling particles according to the present invention can optionally be coated with a catalytically significant quantity of an appropriate catalytic metal or other catalyst material capable of catalytically oxidizing or otherwise degrading waste particulates and/or unburnt hydrocarbons emitted by an internal combustion engine.
Silica and alumina have been found to be catalytically reactive under appropriate conditions. Such particles are believed to be capable of generating highly reactive hydroxyl and other oxidative moieties on their surface under such conditions. In contrast to the generally accepted view that silica and alumina are inert fluidized bed particles, the inventors of the present technology have discovered that an abundance of very reactive hydroxyl radicals and other reactive hydrogen oxide species (and possibly other oxide species) are apparently generated which are capable of catalytically degrading soot, unburnt hydrocarbons and other incomplete combustion products into CO2 and/or water at temperatures below combustion temperatures. It is believed that moisture present in many exhaust streams as well as other organic matter that has been tested creates a surface phenomenon on the silica and alumina particles that actually allows for the catalytic conversion of incomplete combustion products into CO2 and water.
In a preferred embodiment, the silica and/or alumina particles are suspended or fluidized in a fairly static condition against the force of gravity by means of air flowing upwards through the particles. Such airflow can be provided by any gas pressurizing means known in the art, including turbines, pumps, the inherent pressure generated by internal combustion engines, and combinations of the foregoing. Suspending or fluidizing the particles greatly increases the active surface area of the silica and/or alumina particles by separating them slightly and allowing for more gas-to-particle contact. Through chemical mechanisms not wholly understood, the environment immediately on or surrounding the surfaces of the suspended particles is able to catalytically degrade soot, unburnt hydrocarbons and other incomplete combustion products generated by the burning of carbon-containing fuels.
Another advantage of fluidizing, suspending or otherwise separating the silica, alumina or other muffling particulates is that doing so allows for easier flow-through of waste exhaust gases. This, in turn, assists in further reducing back pressure to the internal combustion engine. This results in increased fuel economy and power, with a concurrent decrease in overall emissions generated by the internal combustion engine. Another interesting aspect of the invention is the greatly reduced temperature of the exhaust gases passing through the inventive muffling systems compared to conventional mufflers.
In the case where it is desired for the muffling particles to also catalytically degrade waste particulates and unburnt hydrocarbon gases, the reaction or muffling chamber in which the muffling particles are contained is preferably maintained at a temperature in a range from about 50xc2x0 C. to about 500xc2x0 C., more preferably in a range from about 100xc2x0 C. to about 400xc2x0 C., and most preferably in a range from about 150xc2x0 C. to about 350xc2x0 C. Such temperatures are preferred in view of their being generally within the temperature range of exhaust gases generated by internal combustion engines after passing through the exhaust system. Although such temperatures are preferred, the catalytic oxidation of soot, hydrocarbons and other incomplete combustion products of carbon-containing fuels at any temperature through the use of silica and/or alumina would be within the scope of the present invention. The preferred temperature ranges are also considerably less than the operating temperature within conventional mufflers, which are typically between about 900-1200xc2x0 F.
The heat necessary to maintain the reaction chamber within the desired temperature range can be provided by any source. In a preferred embodiment, the heat will be provided substantially, or even exclusively, by the exhaust gases themselves. Nevertheless, it is certainly within the scope of the invention to supplement the heat found in exhaust gases by means of electric heaters, burning fuels such as methane gas, by recycling heat recovered from other sources, or by any other heat source that is able to provide a desired quantity of heat in order to maintain the reaction chamber within a desired temperature range.
In a preferred embodiment, the means for introducing the waste exhaust gases from the internal combustion engine to the muffling/reaction chamber comprises one or more porous tubes. The term xe2x80x9cporous tubesxe2x80x9d denotes pipes or tubes which include a plurality of holes therein for directing the waste exhaust gases in a desired direction. Preferably, the gas introducing means comprises a plurality of porous tubes radiating outwardly in a spoke-like configuration from a central point, typically an exhaust pipe communicating with the exhaust manifold of an internal combustion engine.
Because of the extreme simplicity of the apparatus used to carry out the muffling/reaction processes of the present invention, it is possible to greatly up-size or down-size the muffling reaction apparatus to accommodate a wide variety of uses and applications. The reaction chambers may be very large or utilized in series in order to serve large industrial needs such as coal or petroleum fired power plants, smelters and the like. The muffling/reaction chambers may be sized for use with diesel engines used to pull trains. They may: be down-sized and adapted for use in catalytically treating exhaust gases produced by conventionally-sized internal combustion engines, e.g., diesel-, gasoline-, and propane-powered engines.
Exhaust gases from the burning of carbon-containing fuels typically comprises incomplete combustion products, which may include carbon soot, gaseous, liquid or particulate hydrocarbons, carbon monoxide, and diatomic hydrogen, among other compounds. Actual laboratory testing has shown that passing exhaust gases produced by a diesel engine through a reaction chamber containing a bed of silica particles greatly reduces both the level of soot produced by the combustion of diesel fuel as well as carbon monoxide. Such pollutants are believed to be converted into CO2 or a mixture of CO2 and water. In addition, nitrogen oxides (NOx) are reduced by about 90%, presumably to nitrogen gas or silicon nitride while carbon, carbon monoxide, and hydrocarbons are being oxidized, presumably to carbon dioxide and water. Perhaps the reactions are interrelated.
Nevertheless, for reasons not entirely understood, even though the levels of carbon, carbon monoxide, and hydrocarbons are greatly reduced using the inventive systems, the measured level of carbon dioxide also appears to drop off, even precipitously in some cases, thus suggesting that the carbon dioxide may be converting to something else, at least temporarily.
The back pressure exerted by the inventive muffling systems is considerably lower than conventional muffling systems. At idle back pressures of about 5 inches of water have been measured, which increase to about 25-30 inches at full load. By comparison, standard conventional mufflers create 40 inches of back pressure at full load.
In view of the foregoing, it is an object of the invention to provide improved methods and systems for effectively and inexpensively muffling the sounds emitted by internal combustion engines while substantially reducing back pressure compared to conventional mufflers.
It is a further object and feature of the invention to provide methods and systems for muffling the sound emitted by internal combustion engines which are simultaneously capable of substantially reducing back pressure compared to conventional mufflers while meeting or exceeding present noise reductions standards.
It is yet another object and feature that such methods and systems for muffling the sound emitted by internal combustion engines are capable of reducing back pressure so as to improve fuel efficiency and increase engine power, while also providing equal or greater muffling of engine sounds compared to conventional mufflers.
It is another object of the invention that such methods and systems for muffling the sound emitted by internal combustion engines are adaptable so as to also be capable of reducing pollutants found in exhaust emissions such that they provide the dual purpose of reducing engine noise and engine pollution.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.